As a conventionally known method for continuously forming a plated coating film, such as a plastic film, on a web while transporting the web, a conductive surface of the web or a metallic web contact is made to contact a cathode roller, and a plating bath in which an anode is placed is provided before or after the cathode roller, so that the plated coating film is formed by the plating bath. In the case where the plated coating film is continuously formed on the web according to the method, wherein the web continuously travels through the unit provided with the cathode and anode, a plated coating film having a desirably large thickness can be easily formed on the web (see the Patent Document 1).
As an example of a substrate used for flexible circuit which has been increasingly often used in an electronic device, an electronic component, a semiconductor package and the like in recent years, a wiring substrate, wherein a polyimide film or a polyester film and a copper foil are bonded to each other, is attracting attention. There are two different types of the substrate used for flexible circuit thus constituted, which are so-called “triple-layered type”, where a copper foil is bonded to the web via an adhesive, and so-called “double-layered type”, where a metallic coating film is formed on the web by means of the plating without any adhesive. Of these two different substrates, the latter “double-layered type” substrate is more spotlighted these days in tandem with the advancements in the miniaturization of circuit wiring pitches.
The current status relating to the substrate for flexible circuit is described below. The triple-layered substrate for print circuit, wherein epoxy-based resin or acrylic resin is used as the adhesive, is disadvantageous in that its electric characteristics are deteriorated due to impurity ions included in the material of the adhesive. Further, in the case where polyimide is used as a base film material, it is not possible to fully take advantage of such a high heat resistance thereof (at least 300° C.) because a heat-resistant temperature of the adhesive is at most 100-150° C. Therefore, it is inevitable to reduce the specification of a heating temperature in the wire bonding for an IC chip for which high temperatures are demanded in the mounting process. In the triple-layered substrate for print circuit, the copper used therein is too thick for such a patterning as at most 80 μm pitch (copper wiring 40 μm, gap 40 μm) because the copper foil is generally as thick as 18 μm or 35 μm, and an etching ratio is thereby significantly reduced. As a result, a large difference is generated between a surface-side circuit width and an adhesive-side circuit width of the copper foil or a whole circuit width is significantly reduced due to the etching, which disadvantageously results in the failure to obtain a targeted circuit pattern.
Therefore, the so-called “double-layered type” substrate was proposed in order to solve the problems in the triple-layered type substrate thus described. The so-called “double-layered type” substrate is obtained such that the electrolytic copper plating is applied after various metals are deposited on the web surface by means of the various deposition processes such as the PVD process such as vacuum deposition, sputtering process or various ion plating processes and so-called CVD process wherein chemicals including metals are vaporized and thereby deposited, or various metals are plated by means of the electroless plating in place of the adhesive. The “double-layered type” substrate is characterized in that a copper film thickness can be arbitrarily changed by the electrolytic copper plating, wherein a 40 μm-pitch circuit pattern can be generated in a simple manner provided that the thickness of the copper film is 8 μm, and heat resistant temperatures of different webs can be directly reflected thereon.
In order to respond to the current status thus far described, there is a high demand for a film having a plated coating film. However, in the conventional method, wherein the conductive surface of the web in contact with the cathode roller is transported as described earlier, scratches and burred protrusions resulting from the scratches may be generated on the conductive surface of the web which is rather vulnerable. Further, an entire length of the cathode roller, which contacts an entire width of the web, is increased as the width of the web is increased, which makes it necessary to increase a diameter of the roller in order to maintain the strength. As a result, the power feeding apparatus is unfavorably increased in size.
The miniaturization of the circuit pattern has been advancing in recent years, and an increasing higher surface quality has been accordingly demanded for the plated coating film. Therefore, the development of a process capable of preventing the generation of very small scratches and protrusions is aggressively moving forward.
The Patent Document 2 proposed a process called a clipping method, wherein an end of the web is nipped with feeding clips, and the end-nipped web is carried through the plating liquid to be plated. According to the method, wherein only the end of the web, which will be removed when the web is finalized as a product, is nipped, no minor scratches or the like are generated in the product, and the surface thereby obtained has a good quality. However, a heavily-developed additional facility, which includes a large-sale transportation system for transporting the feeding clips, a process for removing the plated coating film deposited on the feeding clips and the like, becomes necessary. Further, it is demanded that the plating liquid be as least polluted as possible because foreign matters floating in the plating liquid may disadvantageously roughen the plated surface. However, the plating liquid, in fact, is easily polluted by such foreign matters as abrasion powder because various moving units are placed above the plating liquid. Further, the section nipped with the feeding clips is not plated, and a resistance value is increased because the film thickness of the conductive film is reduced only in the section. As a result, a periphery of the section may be color-changed or altered by the Joule heat generated when large currents are supplied.
The Patent Document 3 recites a plating method wherein a feeding electrode having a plate spring shape is pushed against the end of the web to supply power to the web so that the web is plated. The method can also provide such a good surface quality that scratches or the like are not included in the final product. However, the feeding electrode is easily worn because it is constantly in close contact with the web, and the plating liquid and peripheral devices are polluted by powder generated by the abrasion. Further, the presence of the electrode constantly applies the brake to the web, and a tensile force distribution is thereby generated in the width direction of the web, which may significantly disturb the transportation of the web in a stable manner.
The Patent Document 4 recites an example of a conventional vertical-type plating device in which a feeding electrode having a roller shape is provided. In the example, a feeding electrode having a so-called dumbbell shape in which an outer diameter of the roller at the center is reduced so that both ends thereof alone contact the web was proposed as one of possible shapes of the cathode roller. According to the method, a product, in which the surface flaw such as scratches is reduced at the center of the web not contacted by the roller, can be produced. However, an angular velocity of the roller is equal at the both ends, and therefore, a circumferential velocity is different at the both ends even if a very small difference is generated between outer diameters of the both ends contacting the web. Therefore, a remarkably high working precision is demanded. When the high precision cannot be obtained by any possibility, such a problem that the electrode may be worn or the tensile force distribution may be generated in the width direction because one of the ends slidably contacts the web.
The Patent Document 5 recites a feeding method wherein while any contact of the center of the web is avoided in order to realize the plating without undermining the characteristics of unwoven fabric such as its bulkiness, and only an upper end of the web is exposed out of the plating bath, so that a belt-like electrode is brought into close contact with the exposed part so as to supply power. The method can also provide the plated film having such a high quality that no scratches or bruises are generated at the center, however, the film in the upper end of the web, which is not constantly plated, is very thin and subject to a large resistance. Therefore, the film is color-changed and altered by the Joule heat generated when large currents are supplied. Further, in the case of a web such as a plastic film which is poor in its elasticity in a thickness direction, when the web and the belt-shape electrode are nipped with guide rolls so that they are brought into close contact with each other by a nipping force, a contact resistance between the electrode and the web other than the nipped section is unfavorably increased because they tightly contact with each other only at the guide-roll section. Therefore, heat-related problems may be generated when large currents are supplied.
The Patent Document 6 recites a transporting method, wherein a rotating member having a small width is pressed onto a transportation roller. The rotating member can also serve as the feeding electrode. When the rotating member is set at the end of the web as the feeding electrode according to the method, a product in which flaws are reduced on a surface opposite to a surface tightly contacting the transportation roller can be manufactured. According to the inventors of the present invention, however, the method requires a roller made of a hard material because creases are unfavorably generated on the web by the edge of the electrode in the case where a soft material is used for the transportation roller. As a result, the flaws possibly generated on the surface tightly contacting the transportation roller may not be prevented.
Patent Document 1: No. H07-22473 of the Japanese Patent Application Laid-Open
Patent Document 2: No. 2005-507463 of the Japanese Translation of the PCT Applications
Patent Document 3: No. 2005-248269 of the Japanese Patent Application Laid-Open
Patent Document 4: No. 2003-321796 of the Japanese Patent Application Laid-Open
Patent Document 5: No. H08-209383 of the Japanese Patent Application Laid-Open
Patent Document 6: No. 2004-263215 of the Japanese Patent Application Laid-Open